Servo hydraulic transducer and method of operation

ABSTRACT

An improved servo hydraulic transducer and method of operating is disclosed. The transducer includes a vibrator and hydraulic lifts connected to an improved hydraulic system. The hydraulic system includes a pump pumping hydraulic fluid at a rate between the maximum average and minimum average from a source thereof into a manifold and high pressure system for a frequency sweep of the vibrator. The high pressure system supplies the hydraulic fluid required by the vibrator in addition to that supplied by the pump during the low frequencies of the sweep, and stores under pressure hydraulic fluid excessive to the vibrator requirements during the high frequencies of the sweep and slack time between sweeps. The hydraulic lifts include a chain and sprocket arrangement for each lift interconnected by a synchronization shaft. An unequal force on one of the hydraulic lifts produces through its chain and sprocket arrangement a moment on the synchronization shaft which is transferred through the chain and sprocket arrangement of the other lift to equalize the bearing force between the hydraulic lifts.

United States Patent [191 Bedenbender et al.

1 1 Dec. 30, 1975 [S4] SERVO HYDRAULIC TRANSDUCER AND METHOD OFOPERATION [75] Inventors: John W. Bedenbender, Plano,

Gilbert ll. Kelly, Irving, both of Text.

[73] Assignee: Texas Instruments, Corp., Dallas,

Tex.

22 Filed: Apr. 30, 1973 [21] Appl. No.: 355,838

Primary ExaminerMaynard R. Wilbur Assistant Examiner-T. M. Blum [57]ABSTRACT An improved servo hydraulic transducer and method of operatingis disclosed. The transducer includes a vibrator and hydraulic liftsconnected to an improved hydraulic system. The hydraulic system includesa pump pumping hydraulic fluid at a rate between the maximum average andminimum average from a source thereof into a manifold and high pressuresystem for a frequency sweep of the vibrator. The high pressure systemsupplies the hydraulic fluid required by the vibrator in addition tothat supplied by the pump during the low frequencies of the sweep, andstores under pressure hydraulic fluid excessive to the vibratorrequirements during the high frequencies of the sweep and slack timebetween sweeps. The hydraulic lifts include a chain and sprocketarrangement for each lift interconnected by a synchronization shaft.

An unequal force on one of the hydraulic lifts produces through itschain and sprocket arrangement a moment on the synchronization shaftwhich-is transferred through the chain and sprocket arrangement of theother lift to equalize the bearing force between the hydraulic lifts.

11 Claims, 19 Drawing Figures U.S. Patent Dec. 30, 1975 Sheet 1 0f133,929,206

w NE vv\ w m2 2: $3 m2 U.S. Patent Dec. 30, 1975 Sheet2of 13 3,929,206

US. Patent Dec.30, 1975 Sheet3of13 3,929,206

U.S. Patent Dec.30, 1975 Sheet4of13 3,929,206

MA k Jfli US. Patent Dec. 30, 1975 Sheet6of 13 3,929,206

U.S. Patent Dec.30, 1975 Sheet 10 0f13 3,929,206

R t REACTION MASS M B Fig X F cos (Z 'ft) i PAD I SOIL IMPEDANCE Z r U m2 m I Hg /2 E e db/OCTAVE w o J I l l 1 IDG FREQUENCY, Hz

2 VOLUME FROM 3 ACCUMULATOR m QMAX m M QA VG T T TIME-b 1 US. PatentDec. 30, 1975 Sheet110f13 3,929,206

Fig. /4/] FREQUENCY H l hl T +T TIME (t), SEC

UPSWEEPS 4 FREQUENCY Fig.

(f), Hz

| a T T T TIME (1;), SEC

DOWNSWEEPS U.S. Patent Dec. 30, 1975 FLOW (Q) avg Sheet 12 of 133,929,206

Fig /5 VOLUME FROM ACCUMULATOR, V

T T+T TIME (t). SEC

Fig. /6

PUMP VOLUME AVAILABLE TO CHARGE AccUMULAToR, v

PA 1-QP I PUMP l VOLUME TIME US. Patent Dec. 30, 1975 Sheet 13 0f133,929,206

REQUIRED VOLUME FROM ACCUMULATOR, V GAL.

UQS/ZH L/( 1 aLvu dEIH/SAS Fig.

SERVO HYDRAULIC TRANSDUCER AND METHOD OF OPERATION This inventionrelates generally to improvements in the art of seismographic surveyingof the type utilizing a mechanical vibrating energy source ortransducer,

and more particularly to an improved hydraulically driven system forgenerating continuous seismic signals having swept frequencies.

In the past, many seismic surveying systems have used a continuous waveseismic signal generated in the earth by a vibrator or seismictransducer. These vibrator assemblies generally have been comprised of abase plate or pad retractably mounted upon a truck type vehicle fortransport to a desired field location. Upon arrival at a selected sourcelocation, the pad was lowered by a hydraulic lift mechanism into contactwith the earths surface and then the truck lifted on the pad by thehydraulic lift mechanism to provide a hold down force upon the pad.Prior lift systems have utilized a pair of load bearing columns, a pairof hydraulic lift cylinders and a synchronizing system to insurecoordinated movement of the columns. Where the lift cylinders haveextended above the vibrator, they have been mechanically interconnectedby a rigid stress member; otherwise a hydraulic interconnection systemhas been used for synchronization. The pad was vibrated by a doublerod-end-piston extending upwardly and downwardly in a mass typecylinder. The mass of the cylinder varied from several hundred toseveral thousand pounds. An actuator, usually hydraulic, was used toreciprocate the cylinder mass or reaction mass relative to the baseplate through a short stroke at predetermined frequencies. The equal andopposite force of reaction reciprocated the base plate through a shortvertical stroke at corresponding frequencies, thereby moving the surfaceof the earth and inducing the desired seismic signal in the earth.

The hydraulic actuator consisted of a pump pumping oil under highpressure from a reservoir through a manifold into a high pressureaccumulator and through a servovalve for selectively introducing oilinto the cylinder. Oil from the high pressure system was alternatelyintroduced by the servovalve into the cylinder above and below thepiston to vibrate the weight bearing cylinder. The oil was returnedthrough the servovalve alternately from below and above the piston intoa low pressure accumulator used for dampening oil surges prior toforcing the oil into an oil cooling system for cooling the oil before itwas returned to the high pressure system by the pump. The high pressureaccumulator in prior system has been a relatively small volumeaccumulator and used only to smooth out the peaks of the sinusoidalsupply required by the vibrator. The pump capacity (0,) was fixed atapproximately the average flow (Q required for the lowest desiredoperating frequency (f,) using the following formula:

where p hydraulic pressure, psi A hydraulic piston area, in f theoperating frequency, Hz M, reaction mass, (lb sec)/in 2 The highpressure accumulator size was determined at the lowest operatingfrequency. The accumulator had to supply a volume equal to thedifference between the instantaneous peak flow (O and the average flow(0 required by the vibrator during the period (T,) of the lowestoperating frequency. This volume is represented by the followingformula:

V: 0.59 T, On, in."

A problem with the prior art is the large size of the hydraulic systemrequired for a mechanical vibrator to produce desired seismicvibrations. A further problem lies with the lift system which is proneto seizure when the mechanical vibrator pad is positioned on unevenearth surfaces.

Thus it is an object of the present invention to pro vide an improvedtransportable seismic transducer assembly.

Another object of the invention is to provide a seismic transucerassembly with an improved mechanical synchronizing system for insuringcoordinated movement of the lift columns with the hydraulic lift system.

Still another object of the invention is to provide an improvedhydraulic system for a seismic transducer in which high pressureaccumulators are used to supply a major part of the high hydraulic flowfor the low frequency portion of the sweep to approximately double theeffective power output of the transducer.

Briefly stated the transportable seismic transducer constituting thesubject matter of the present invention comprises a vehicle such as, forexample, a truck, tractor or tractor drawn trailer supporting aretractable novel transducer or vibrator system. The rectractabletransducer is suspended by a pair of hydraulic lifts having a novelmechanical synchronizing system to insure coordinated movement ofcolumns of the hydraulic lifts.

In accordance with a more specific aspect of the present invention, thetransducer of the portable transducer has a base plate or pad which islowered into contact with the earth by means of the hydraulic liftsmounted upon the transporting vehicle. After bringing the pad intocontact with the earth, the hydraulic lifts raise the vehicle on the padto provide a hold down force for maintaining the pad in contact with theearth during vibration of the transducer. The novel mechanicalsynchronization system for the hydraulic lifts includes a chain andsprocket arrangement for each hydraulic lift. The chain from onehydraulic lift runs over a sprocket at one end of a synchronizationshaft, and the chain from the other hydraulic lift runs over a sprocketat the opposite end of this shaft. An unequal force on one of thehydraulic lifts produces through its chain and sprocket arrangement amoment on the synchronization shaft which is transferred through thechain and sprocket arrangement of the other lift to the other lift toequalize the bearing force between the hydraulic lifts.

With the base plate or pad anchored to the ground the vibrator isvibrated to send out into the earth through the pad a series ofvibratory sweeps". These sweeps are ordinarily a linear change offrequency with time. Each sweep may be from a low (about 5H2) to a high(about Hz) frequency upsweep or a high to low frequency down sweep. Thevibrator includes a weighted cylinder, often referred to as the reactionmass, reciprocately mounted on a double rod-end-piston having the endsthereof connected to the base plate. The cylinder or reaction mass isreciprocately actuated by pressurized hydraulic fluid introducedalternately in the cylinder above the below the piston. The novelhydraulic system comprises a pump capable of pumping a prescribed amountof the total hydraulic fluid required for each sweep and a high pressureaceu mulator system having sufficient capacity and pressure force toprovide the remainder of the total fluid required for each sweep.

It has been found that with the practice of the present invention thehydraulic pump and engine used to drive the vibrator of the prior artdevice can be reduced more than one-half in capacity and produce thesame results as the prior art devices, or for the same hydraulic pumpand engine the displacement amplitude of the reaction mass can beapproximately doubled to increase the amplitude of the seismic signal.Further objects and features of this invention will become obvious fromthe following description when taken in conjunction with the drawings inwhich:

FIG. 1 is a side view of a buggy mounted transducer constituting anembodiment of the present invention;

FIG. 2 is a top view of the buggy mounted transducer shown in FIG. 1;

FIG. 3 is an end view of a transducer constituting an embodiment of thepresent invention;

FIG. 4 is a partial cross-sectional view of the transducer taken alonglines 44 of FIG. 2;

FIG. 5 is a partial elevational view with portions broken away to showdetails of one of the hydraulic lifts;

FIG. 6 is a cross-sectional view of the hydraulic lift of FIG. 5 takenalong line 6-6 of FIG. 5;

FIG. 7 is a partial view of the hydraulic lift synchronization and liftcontrol system;

FIGS. 8A and B are schematic diagrams of a hydraulic system for thevibrator or transducer assembly constituting an embodiment of thepresent invention;

FIG. 9 is a cross-sectional view of the high pressure accumulatorutilized in the hydraulic system shown schematically in FIG. 8;

FIG. 10 is a schematic drawing of the electronic controller for thetransducer;

FIG. I] is a schematic model of the vibrator transducer;

FIG. 12 is a plot of required hydraulic flow versus transducer operatingfrequency;

FIG. 13 is a plot of flow versus time for a fixed frequency;

FIGS. 14A and B are representations of frequency sweeps versus time;

FIG. 15 is a plot of hydraulic flow versus time for an upsweep;

FIG. 16 is a plot showing the hydraulic flow pattern plotted againsttime;

FIG. 17 is a plot showing the required volume from the high pressureaccumulator plotted versus sweep rate.

Referring now to the drawings for a detailed description of the improvedportable seismic transducer assembly in which there is shown (FIG. 1) avehicle 10 having front and rear wheels 12 and I4, respectively, whichsupport a chassis comprised generally of frame channels 16, a cab 18,and a conventional engine 20. The engine 20 is connected to drive therear wheels 14 by a conventional drive train including a drive shaft 22.

The seismic transducer or vibrator assembly 24 (FIGS. 1 and 3) isdisposed between the front and rear wheels and connected to the framemembers I6 of the truck by a lift system 26 hereinafter described. Aprime moveror engine 28, main hydraulic pump 30, high pressureaccumulator system 32, low pressure accumulator system 34 (FIG. 2),hydraulic fluid tank 36, hydraulic fluid cooler 38 and associatedhydraulic plumbing may be located on the frame members I6 as shown inFIGS. 1 and 2.

The transducer or vibrator assembly 24 (FIG. 3) includes a base plate orpad 40 which may be fabricated in any suitable manner to provide a flatlower base plate surface for engaging the surface of the ground. Atransducer frame 42 comprising four vertically disposed frame members 44extends upwardly from the base plate 40 to a point well above the driveshaft 22 of vehicle 10 (FIG. I). The lower halves of the four framemembers 44 (FIG. 3) are reinforced by gusset plates 46. Bottom footplates 48 are connected to the four vertical members of the frame 42 andthe frame is bolted or otherwise attached to the base plate member 40.Top plates 50 are connected to the tops of the frame members 44 and arebraced by gusset plates 52.

An upper cross-member 54 is formed by intersecting channels 56. Theouter ends of the channels 56 are bolted to their respective top plates50 by bolts 58. A lower cross-member 60 is constructed similarly to theupper cross-member 54 in that it comprises intersecting channel members62 having their outer ends welded to points intermediate the fourtransducer frame forming vertical members 44. The intersections of theupper and lower cross-members 54 and 60 are adapted to receive the endsof a double rod-end piston member 64. The upper and lower ends of therods of the piston member 64 are securely connected to the intersectionsof the cross-members 54 and 60, respectively, by a plurality of bolts orscrews 66.

The piston member 64 has a piston (FIG. 4)'

within a cylinder 72 formed within a reaction mass 74. Piston 70 isprovided with conventional piston rings 76 for insuring a sliding,fluid-tight seal with the interior of the cylinder 72. Hydraulic fluidis introduced into the cylinder 72 alternately on opposite sides of thepiston 70 from a manifold control means such as, for example, a standardfour port servo control valve 78 directing high pressure oil alternatelythrough upper and lower hydraulic ports 80 and 82. High pressure oil issupplied to the servovalve through a high pressure passage 71 and lowpressure oil flows from the servovalve through passage 73. Passages 71and 73 are connected by hoses to a manifold 232 (FIG. 1) external toreaction mass 74 (FIG. 4). Thus, it will be evident that as hydraulicfluid is introduced through the lower port 82 into the cylinder 72 (FIG.4) below the piston 70 the reaction mass 74 is driven downwardlyrelative to the piston member 70, and therefore relative to the pad 40(FIG. 3). Conversely, when hydraulic fluid is introduced through theupper port 80 (FIG. 4) into the cylinder above the piston 70 thereaction mass 74 will be driven upwardly. As the reaction mass 74 isdriven downwardly, an upwardly directed reaction force is applied to thepad 40 (FIG. 3) and when the reaction mass is driven upwardly, adownwardly directed reaction force will be applied to the pad 40. Theamount of hydraulic fluid introduced into the cylinder 72 (FIG. 4) iscontrolled to vibrate the reaction mass 74 to produce varyingfrequencies of a given frequency range of a sweep.

In normal operation, the reciprocation of the reaction mass 74, (FIGS. 3and 4) is maintained centered between the upper and lower cross-members54 and 60 by means of a linear variable-differential transducer (LVDT)84 (FIG. 2) having its electrical coils (not shown) mounted in a wellprovided therefor in the reaction mass 74 (FIG. 3). These coils surrounda core member (not shown) which is attached to the lower cross-membcr60. The electrical output of the LVDT 84 is coupled to an electronicscontroller hereinafter described (FIG. Additional reaction mass supportis provided by a pair of strut type arrangements 90 (FIG. 4) mounted inthe reaction mass 74. Each strut arrangement (FIG. 4) includes acylinder 92 having its upper end connected to a hydro-pneumaticaccumulator 94 such as, for example, Greer Hydraulics Inc., Model No.AIO8-200. The accumulator is pressurized with a suitable gas such asnitrogen to a pressure of 1,500 psi. A rod type piston 96 having abearing end 98 in engagement with a stop plate 100 (FIG. 3) attached tothe lower cross-member 60 is mounted in the cylinder 92 (FIG. 4). Thevolume of the cylinder 92 above the rod type piston 96 and the oilvolume of the accumulator is filled with oil and connected by a passage(not shown) to a high pressure passage 71. A substantially constantforce occurs to aid in centering the reaction mass about the vibratorpiston 70 (FIG. 4). Nevertheless, to guard against the eventuality thatthe reaction mass member 74 may become uncentered and strike either ofthe upper or lower cross-members, bumper studs 102 (FIG. 4) of a pair ofshock absorbers 104 extend outwardly from each of the upper and lowerfaces of the reaction mass 74 to engage the upper and lowercross-members 54 and 60 (FIG. 3) to cushion and dissipate any strikingforce of the reaction mass 74.

To prevent the reaction mass 74 from rotating around the piston member70, two anti-rotation plates 105 are attached to two of the transducerframe members 44 which upon rotation of the reaction mass 74 engage theedges of the reaction mass 74. The transducer frame members 44 andanti-rotation plates 105 thus act as rotation stop members for thereaction mass 74.

A novel synchronized hydraulic lift system 26 (FIGS. 1, 2 and 5)interconnects the transducer to the vehicle frame members 16. Thissystem is comprised of two identical lift units 107 and 109 (FIG. 2)disposed on opposite sides of the transducer; each lift unit is mountedin a bushing box assembly 110 (FIG. 5) attached to frame members 16. Asthe lift units and attachment journals are similar only one of each needbe described. The bushing box 110 (FIGS. 5 and 6) comprises a first pairof oppositely disposed plates 112 which are parallel to the framemembers 16 and a second pair of oppositely disposed plates 114 which arenormal to the frame members 16. Plates 114 extend beyond plates 112 toform ear portions 114a and 1l4b. Ears 114a are bolted to angle irons 116which are rigidly secured by bolts or welds to one of the vehicle framemembers 16. Bars 11411 and angle irons 118 attached to plate 120 supportgussets 121 extending upwardly of the casing 150 (FIG. 5) in supportthereof. Angle irons 116 have a channel bar 119 (FIG. 6) attachedbetween them to support a pair of idler sprockets 122 and 124 (FIG. 5)in a vertically spaced and aligned relation one to the other for a liftsynchronization chain and sprocket arrangement hereinafter described.Portions of the channel 119 and angle irons 116 are cut away to provideopenings therein for feed- 6 ing a chain (FIG. 7) to the idler sprockets122 and 124 (FIG. 5).

The hydraulic lift unit includes a hydraulic lift cylin der 126 slidablymounted within a bushing 106 which is a part of bushing box 110. Thelift cylinder 126 has its lower end connected adjacent a side of pad 40by a vibration isolation means 128 (FIGS. 1 and 3). The vibrationisolation means permit a static hold down load to be applied to the baseplate 40 while permitting free vertical reciprocation of the base platerelative to the truck to isolate the truck from the vibrating structureand also for transmitting a tension force from the vertical lift columns126 to the base plate 40 so that the transducer or vibrator assembly 24can be lifted for transport. Each isolation means 128 (FIG. 1) comprisestwo lower mounts 132 for supporting a pair of air springs 136 and anupper shoe 140. The upper shoe 140 has its lower face engaging the upperends of the air springs 136 and its upper surface connected to thehydraulic lift cylinder 126. To prevent lateral displace ment of thehydraulic lift cylinder 126 relative to the base plate 40 throughlateral movement of the air springs 136, three tie rods 142, 144 and 145(FIGS. 1 and 3) are positioned at ends of the vibrator isolation means128. Each tie rod 142, 144 and 145 has one end pivotally connected tothe base plate 40 and its other end pivotally connected to the uppershoe 140 adjacent its outer edge. To relieve stress on the air springsduring lift of the vibrator pad 40, a pair of chains 146 are attached ateach air spring to the sides of the upper shoe 140 and to the base plate40.

The lift cylinder 126 (FIG. 5) is mounted in an outer casing 150 whichterminates at the bushing box 110 and is fastened with the bushing box110 to the vehicle frame member 16. The upper end of the casing 150 isclosed by a flanged annular cap 154 in which is mounted the rod 156 oflift cylinder 126. The rod 156 is retained in position by a pivot shaft160 passing through the lift unit casing 150 and cap 154 and retainedtherein by retaining rings 162. A piston (not shown) is attached to rod156 in the cylinder 164 of the lift cylinder 126. Hydraulic fluid isintroduced into the lift column cylinder above and below the piston toforce the lift cylinder 126 selectively either downwardly to lower thepad 40, to raise the truck from the ground, or upwardly to raise thepad.

The novel lift system described above thus uses a lift cylinder which isalso the load bearing column. In prior art lift systems a hydraulic liftcylinder separate from and eccentric to the lift column is used. A priorart lift system is shown in US. Pat. No. 3,306,391 issued 28 Feb. I967.The novel lift synchronizing means de scribed hereinafter may be usedeither with a prior art lift cylinder and column arrangement or with thenovel lift cylinder arrangement described herein.

The novel mechanical synchronizing system (FIGS. 1 and 7) is forsynchronizing the operation of the hydraulic lift units and thereforethe raising and lowering of the opposite ends of the pad 40. It will beappreciated that if the vibrator pad 40 comes to rest upon uneven groundor if a portion of it comes to rest upon a protruding rock or log, oruneven distribution of the lowering force and hold down force on thehydraulic lifts will result. If this unequal force is not equalized, onehydraulic lift will assume a greater share of the work required to liftthe truck assembly; such unequal stress could result in a seizing of thelift columns. A function of the mechanical synchronizing system is toequalize the operating forces on the hydraulic lift units.

The novel mechanical synchronizing system comprises a sprocket and chainarrangement for each lift coupled to a synchronizing shaft 166 (FIG. 7)mounted in the vehicle frame members 16. Each sprocket and chainarrangement is identical, thus only one is described. The sprocket andchain arrangement comprises: the idler sprockets 122 and 124, which aspreviously mentioned are mounted in the lift column assembly chassisattachment box means 110 (FIG. a sprocket 168 (FIG. 7) mounted on an endof the synchronizing shaft 166; a first adjustable chain support clamp170 (FIG. 5) rigidly secured to the lift cylinder 126 adjacent its upperend and in line with the idler sprockets 122 and 124; a secondadjustable chain support clamp 172 (FIG. 7) attached to the upper shoe140 at the lower end of the lift cylinder; and a chain 174. Thesynchronizing shaft 166, being journaled in the frame members 16 behindthe lift mechanism and on the centerline between the idler sprockets 122and 124, the sprocket 168 is positioned rearwardly of the idlersprockets and intermediately to them. Chain 174 has one end attached tothe first or upper chain support clamp 170 (FIG. 5) and runs along thelift column casing 150, around idler sprocket 122 (FIG. 7), along thevehicle frame member 16, around sprocket 168 back along the vehicleframe member 16, around idler sprocket 124 and along the lift column tothe lower chain support clamp 172.

It will be appreciated that, with each hydraulic lift equipped with theabove described chain and sprocket arrangement, the lift carrying weightin excess of the weight carried by the other lift will transfer throughsprocket 168 an equalization force or moment to the synchronizationshaft 166 and through the chain and sprocket of the other lift to theother lift column to synchronize lift column movement and to equalizethe loads between the lifts.

The mechanical synchronizing system includes a novel lift controlmechanism on one side of the vehicle only which includes one or morecams adapted to coact with one or more switches to control the operationof the hydraulic lifts. The control mechanism as shown (FIG. 7) includesthree cams 176, 178, and 180 and three limit switches 182, 184 and 186.The cams 176-180 are positioned on that portion of chain 174 extendingbetween sprocket 168 and sprockets 122 and 124 and have arms extendingoutwardly away from the chain in a spaced relation one to another toengage the three limit switches 182-186. The switches are mounted in avertical line upon a channel 188 attached to one of frame members 16adjacent the side of sprocket 168 nearest to idler sprockets 122 and124. Each switch 182-186 includes a rocker arm outwardly spaced one toanother to align rollers mounted on the ends of the arms withcorresponding cams 176-180 for engagement selectively with the cams. Thecams 176-180 are positioned typically on the chain 174 as follows: withthe lift assembly in the full up position cam 176 is positioned adjacentsprocket 122, cam 178 is positioned adjacent sprocket 168 and cam 180 ispositioned immediately before cam 178. Cam 176 and switch 182 arereferred to as a pad half lift cam and switch. Cam 176 is so positionedwith respect to switch 182 that movement of the cam 176 with aprescribed amount of lift travel (about inches) from the full upposition will trip switch 182 to lift the pad 40 a desired distance offthe ground. With cam 176 in this position,

minimum pad lift is obtained; to increase pad ground clearance the cam176 is moved toward the sprocket 168. The cam 178 and switch 184 arereferred to as a sweep interlock cam and switch. Additional lift travel(about 5 inches) from the full up position brings cam 178 in contactwith switch 184 to activate the switch and enable an electroniccontroller for the transducer after the pad hits the ground and thetruck is partially lifted (about 2 inches). This switch alleviates thepossihility of activating the vibrator while the pad is in the air. Bymoving cam 178 toward sprocket 168, the interlock switch will be trippedlater, that is, at a lower pad position; by moving the cam 178 away fromsprocket 168 the interlock switch will be tripped earlier, that is, at ahigher pad position. Cam 180 and switch 186 are referred to as a truckhalf lift cam and switch. Farther lift travel (about 2 inches) willcause cam 180 to trip switch 186 and stop the truck a farther distance(about 4 inches) off the ground. For more truck lift, cam 180 is movedaway from sprocket 168 and conversely, for less truck lift cam 180 ismoved toward the sprocket 168. The chain and sprocket arrangement can beconstructed so that for a chain pitch of one inch, the movement of cam180 one chain link on the chain will result in a 1 inch change in padlift. For adjustments of less than one inch, all three cams may be movedby adjusting the adjustable chain clamps 170 and 172 on the top of thelift column and on the foot piece.

For transporting the seismic transducer without assistance of thehydraulic lift system, a pair of support frames 190 and 192 (FIGS. 1 and2) are provided to support the transducer 24 in the raised position. Thesupport frames 190 and 192 are similar in construction and comprisetubular members welded into a trapezoidally or square shaped frame ofwhich one side 194 forms a tubular axis member which is pivotallyconnected to the vehicle frame 16 by a pair ofjournals 196 and 198. Dogs200 are attached to the transducer frame 42 so as to engage the uppermember of frame 190 and support the transducer assembly 24 at the properheight. The journals 196 and 198 are positioned on the frame of thetruck so that the pivotal support frame may be retracted from thetransducer and remain back against the lift column assembly so as not toimpair operation of the vibrator.

The hydraulic lifts and transducer cylinder 72 (FIG. 4) are providedhydraulic fluid by a hydraulic system shown schematically in FIGS. 8Aand B. The operation of the hydraulic system will first be described.Then the basis for and operation of the novel part of the hydraulicsystem which is one object of this invention will be described.

The hydraulic system (FIGS. 8A and B) comprises a hydraulic fluidcontainer 36, hereinafter referred to as tank 36, equipped with afillerbreather 201, a tank drain 202, and a suction filter 204. An oilline 206 couples the tank through a tank shut off valve 208 to a primepump 210. The prime pump 210 may be an electrical pump operated from thebattery of the vehicle. The prime pump 210 pumps oil into a low pressureWith the pressure in the low pressure line at 150 psi, the main pumpdriver or engine 28 (FIG. I) is started and the prime pump 210 (FIG. 8A)is shut off automatically by a prime pump shut off pressure switch 216.The engine 28 drives charge pump 218 to maintain the pressure in the lowpressure system at about I50 psi. Charge pump 218 is provided with arelief valve 220 which is set at approximately I80 psi as an additionalprotection means. The oil pumped by charge pump 218 makes up anyinternal leakage in the system and the remainder is dumped by reliefvalve 214 through the case of pump 30 back to tank 36 thus affordingcooling for pump 30. The speed of engine 28 is then increased and thepump displacement control 222 of the main pump 30 is moved to the openposition thereby permitting the main pump 30 to pump oil from the lowpressure system into a high pressure system. The pump displacementcontrol 222 is provided with a pressure override control which is setfor 3,000 psi pump pressure to maintain pressure within the highpressure system at 3,000 psi. If the pressure within the low pressuresystem ever falls below I psi, a pressure switch 224 which is set at I00psi is activated to shut down the main pump engine 28. The pressure ofthe high pressure system is measured at the main pump output by gage 226(FIG. 88) mounted in the panel of vehicle cab 18.

The low pressure side of the main pump 30 (FIG. 8A) is coupled to theoutlet of the low pressure system. The low pressure system has as itsinlet the low pressure port of the servovalve 78 (FIG. 8B). Theservovalve 78 is attached to the vibrator cylinder 72. The low pressureport of servo valve 78 is coupled through a vibrator cylinder shut offvalve 228 to the low pressure side 230 of manifold 232. The low pressureside of the manifold 232 has a prime pump check valve 234 coupled toprime pump 210, to allow prime pump 210 (FIG. 8A) to charge the lowpressure system but to keep low pressure system oil from feeding back tocharge pump 210 when it is shut off. The low pressure outlet of manifold232 (FIG. 8B) is coupled to two low pressure accumulators 236 and 238(FIG. 8A) adjacent to the manifold for removing surges in fluid flow outof the manifold and to a third surge preventing accumulator 240 locatedadjacent to the oil cooler 38 for removing any reverse fluid flow surgesin the low pressure system resulting from the introduction of the fluidinto the oil cooler 38. The accumulator 240 is coupled to the junctionof an oil cooler inlet 24] and a cooler bypass valve 242. An oil cooleroutlet 244 is coupled to the junction of the cooler bypass valve 242 andto another surge preventing accumulator 246 to further dampen any surgesoccurring in the low pressure system. The accumulators 236, 238, 240 and246 may be, for example, Greer Hydraulic Inc. Hydro-PneumaticAccumulator, Model No. 30A5TB, charged to a gas pressure of 90 psi whensystem has zero pressure. The outlet of the accumulator 246 is coupledto a filter 248 to remove any contaminate particles larger than 3microns in size. The outlet of the low pressure filter 248 is coupled tothe low pressure side of the main pump 30. The low pressure side of themain pump 30 is connected to an oil temperature gauge 250 (FIG. 88)located on the panel of the vehicle cab 18. The oil cooler 38 (FIG. 8A)is provided with an air bleed pipe 252 which is coupled to the tank 36(FIG. 88) to aid in removing air from the hydraulic system. The oilcooler 38 (FIG. SA) has a second outlet 254 coupled also to the reliefvalve 214.

10 The relief valve 214 being set at psi opens at that pressure topermit oil to flow from cooler outlet 254 through the case of main pump30 into the tank 36.

The high pressure side of main pump 30 is coupled to the input of thehigh pressure system. The high pressure system comprises the main pumpoutlet which is coupled to a filter 256 to remove any particles ofapproximately 3 microns or above in size. The filter output is coupledto a high pressure check valve 258 (FIG. 8B) located at the highpressure side 260 of manifold 232. The high pressure check valve is toremove any surges in the high pressure system for reflecting back to thepump. The high pressure side 260 of manifold 232 is coupled to a highpressure accumulator system 262 (FIG. 8A) and to the high pressure portof servo valve 78 (FIG. 8B) which controls injection of the highpressure fluid into the vibrator cylinder 72 of transducer 24 (FIG. 3).The piston in the vibrator cylinder 72 divides the high pressure systemfrom the low pressure system at one end of the hydraulic system and themain pump 30 (FIG. 8A) acts to divide the high pressure and low pressuresystems at the other end of the hydraulic system. The high pressureaccumulator system 262 comprises a pair of accumulators 264 and 266. Thehigh pressure accumulators 264 and 266 may be Greer Hydraulics Inc.Hydro-Pneumatic Accumulators, Model No. 3OA-5TB. These hydro-pneumaticaccumulators have a nominal fluid volume 265 of 5 gallons and a gasvolume 263 of 1,095 cubic inches and are constructed as shown in FIG. 9.The hydro-pneumatic accumulators are modified to increase their volumeof gas by connecting their gas bladder ports to a plurality of gasbottles 268 (FIG. 8A). Each gas bottle has a volume of approximately1,800 cubic inches. The gas volume of gas bottles 268 and the gasbladders of the high pressure accumulators 262 and 264 are filled with asuitable gas such as, for example, nitrogen at a pressure of 2,800 psiprior to actuation of the high pressure pump. With the pump producing apressure above that of the accumulators, e.g., 3,000 psi, the pumpforces oil into the oil chambers of the accumulators 264 and 266 tocompress the nitrogen in the bladders and bottles to an equalizingpressure of 3,000 psi. The novel usage of the high pressure accumulatorsand nitrogen supply, to be described in more detail hereinafter, is oneway in which the improved transducer of this invention is distinguishedfrom prior art transducers. The oil pressure in the high pressure side260 of the manifold 232 is measured by a high pressure accumulator oilpressure gauge 270 (FIG. 88) mounted in the panel of vehicle cab 18. Abypass valve 272 is coupled to the high pressure side 260 of manifold232 to allow bypassing oil from high pressure to low pressure systemswith out passing through vibrator cylinder 72. Bypass valve 272 isclosed when the vibrator is in operation. To protect the high pressuresystem against damaging high pressure, a relief valve 273 is set at3,600 psi. The outlet of relief valve 273 is coupled to the low pressureside of manifold 232. To protect the low pressure system from damagingpressure a relief valve 274 is coupled to the low pressure side ofmanifold 232. The relief valve is set to open at 240 psi and the outletof the valve is connected to the tank 36 so that oil escaping throughthe relief valve is collected in the tank.

The hydraulic system for the hydraulic lifts of the transducer comprisesa lift valve 276 coupled to a high pressure port of the manifold 232 andto an adjustable pressure reducing valve 278. The pressure reducingvalve 278 may be adjusted to introduce oil under pressure to the lowerportion of the lift cylinders to provide a desired truck lift pressureto the lift units 107 and 109 (FIG. 2). Oil from the lift units 107 and109 is returned through the lift valve 276 (FIG. 88) to a low pressureport of manifold 232. Oil under high pressure is also coupled from thelift valve 276 through line 280 to the upper or pad lift side of thelift cylinders of lift units 107 and 109 (FIG. 2).

The operation of the transducer assembly is controlled by an electronicscontroller 282 (FIG. having its output coupled to a torque motor 284 ofservo valve 78. Because of the high flow rate involved in the system ofFIG. 8, the servo valve 78 is a three stage valve. The first stage 286which might be a flapper valve stage is coupled to the torque motor 284and to the second stage 288; the second stage is coupled to the thirdstage 290, and the third stage output is controlled by a slidable spoolmember for selectively introducing oil into the vibrator cylinder 72.The slidable spool member reciprocates to alternately open and close thehigh pressure channel leading to the upper and lower portions of thevibrator cylinder 72 while closing and opening alternately the upper andlower portions of the vibrator cylinder 72 to the low pressure returnchannel of the servo valve. The spool of the third stage 290 is coupledto a linear variable-differential transducer 292 whose output is fedback to the electronic controller 282. The electronic controllercombines the information from the LVDT 84 mounted in the vibratorcylinder 72 and with information from an accelerometer (not shown)attached to the transducer frame 42 and produces an adjusted sweepsignal for proper control of the torque motor 284. The electroniccontroller 282 may be, for example, a T1 controller available under PartNo. 139,066-2 which includes a function generator for generating sweepsignals within the transducer assembly 10, or it may be anElectro-Technical Laboratorys Model No. SHV200 Controller. The Electro-Technical Laboratorys Model No. SHV200 includes a receiver for receivingsweep signals generated remotely to the transducer assembly 10.

In operation the transducer truck 10 is moved to a marked sourcelocation in an area of seismic operation and the hydraulic system isactivated as follows. The electric prime pump 2l0 is activated topressurize the low pressure side of the hydraulic system to about 150psi. At this point the main pump engine 28 is started and the prime pumpshut off. The main pump 30 pumps oil from the low pressure side into thehigh pressure side to pressurize the high pressure side to about 3,000psi pressure. When the high pressure has reached 3,000 psi, oil has beenstored on the oil side of the accumulators 264 and 266 until thepressure on the gas side is raised from its inactive pressure (2,800psi) to its force equalizing pressure of about 3,000 psi; at this pointthe pressure in the manifold will also be 3,000 psi.

The hydraulic system having been brought up to pressure is ready tooperate the transducer assembly. The hydraulic lift units 107 and 109are activated by opening the lift valve to permit oil to flow from thehigh pressure side of manifold 232 through line 280 into the hydrauliclift units 107 and 109 to raise the transducer assembly 24 off the framesupport 190. The frame support I90 is then pivoted away from thetransducer assembly 24 to clear it for operation. The lift valve 276 isthen reversed to permit oil to flow from the high pressure side ofmanifold 232 through reducing valve 278 to lift units 107 and 109 tolower the base plate from its raised position into contact with theground and to raise the truck off the ground until the truck half liftcam trips the truck half lift switch 186 to stop the hydraulic liftsystem. When the lift synchronizing chain 174 has reached this position,the sweep interlock cam 178 has tripped the sweep interlock switch 184to enable the vibrator controller to operate.

With the pad 40 firmly held down by the truck, the electronic controller282 feeds sweep information to the servo valve torque motor tomanipulate the servo valve to selectively introduce oil into thecylinder 72. The control electronics 282 utilizes the three feedbackloops of sensors 292, 84 and 293 (FIG. 10) to cause the transducer tooperate in accordance with the desired sweep signal.

Having described the operation of the hydraulic system in general it isappropriate to further describe the novel high pressure accumulatorsystem and distinguish it from prior art.

FIG. 11 shows a much simplified model of the vibeator transducer. F cos(2 1r ft) is the alternating force imposed by the hydraulic cylinderbetween the reaction mass M and the ground pad; f is frequency, Hz, andt is the time/sec. The soil impedance Z, is a complex function of earthproperties and frequency; however, it is usually assumed for designpurposes that the soil impedance plus the mass of the ground pad islarge and thus that the ground pad has no displacement (X, 0). This isnot strictly true, of course, but it has been found that the zero paddisplacement model is adequate for specifying hydraulic systemparameters.

From FlG. H with X, 0 it is seen that the displacement and velocity of Mare, respectively F cos (21rft) The force amplitude exerted by thehydraulic piston is F pA when p hydraulic pressure, psi, and A hydraulicpiston area, in. The flow supplied to the hydraulic piston must be o pA'sin (21ft) Q AX. Zn/Ml in sec.

The peak flow is pacity.

1. A transportable hydraulic seismic transducer comprising: a. atransport means for transporting hydraulic seismic transducer; b. avibrator means attached to the transport means, for producing mechanicalvibrations; c. a pad rigidly secured to the vibrator for generatingacoustical energy in the earth responsively to the vibrations of thevibrator; and d. a hydraulic system means operatively connected to thevibrator means for vibrating the vibrator to produce varying frequenciesthrough a given frequency range for a sweep, including (i) a source ofhydraulic fluid, (ii) pump means connected to the source of hydraulicfluid for pumping continuously throughout the sweep hydraulic fluid fromthe source at a volume rate less than the maximum average volumerequired for the vibrator to produce the varying frequencies of thesweep; (iii) a power source connected to the pump for driving the pump;(iv) a high pressure accumulator coupled to the pump means for storinghydraulic fluid under pressure between sweeps and during the period ofthe sweep at which the pump volume exceeds the requirements of thevibrator means; (v) manifold means coupled to the pump means and highpressure accumulator for alternately introducing hydraulic fluid intoand withdrawing hydraulic fluid from the vibrator means; and (vi) acontrol means connected to the manifold means for controlling the amountof hydraulic fluid introduced into the vibrator whereby the vibrator isactivated to produce the varying frequencies of the sweep.
 2. Atransportable hydraulic seismic transducer comprising: a. a transportmeans for transporting a hydraulic seismic vibrator to a seismic sourcelocation; b. a vibrator means for producing mechanical vibrationsmounted upon said transport means; c. a pad rigidly secured to thevibrator for generating acoustical energy in the earth responsively tothe vibrations of the vibrator; and d. a hydraulic system meansoperatively connected to the vibrating means for vibrating the vibratorto produce varying frequencies of a given frequency range of a sweepincluding: (i) a hydraulic fluid pumping means connected to the vibratormanifold for supplying the manifold with hydraulic fluid continuouslythroughout the sweep at a volume rate less than the maximum averagevolume required for the vibrator to produce the varying frequencies ofthe sweep; (ii) pressurized storage means coupled to the manifold forstoring hydraulic fluid under pressure between sweeps and during theperiod of the sweep the volume supplied the manifold exceeds thevibrator means requirements; and (iii) a control means connected to themanifold means for controlling the amount of hydraulic fluid introducedand removed from the vibrator means whereby the vibrator is activated toproduce the varying frequencies.
 3. A transportable seismic transducercomprising: a. a transport means for transporting a hydraulic seismicvibrator; b. a vibrator means for producing varying frequencies througha given frequency range of a sweep, said vibrator means carried by saidtransporting means; c. a pad rigidly secured to the vibrator means forgenerating acoustical energy into the earth responsively to thevibration frequencies of the vibrator; d. a pair of lift columns mountedupon the pad and slidingly secured to the transport means in positionsto extend substantially vertically on opposite sides of the transportmeans; and e. hydraulic means carried by the transport means foractuating the lift columns and vibrator means for selectively raisingand lowering the columns relative to the truck and for raising andlowering the transporting means as to the lift columns and foractivating the vibrator means to produce varying frequencies of a givenfrequency range of a sweep, said hydraulic means including; (i) meansfor supplying hydraulic fluid to a manifold for the lift columns andvibrator means at a volume rate between the maximum average and minimumaverage volume required for the vibrator to produce the varyingfrequencies of the sweep; (ii) selective means connected to the manifoldfor introducing selectively hydraulic fluid into lift cylinders of thelift columns and into the vibrator means; (iii) a pressurized storagecontainer coupled to the manifold for storing hydraulic fluid underpressure during the slack time between sweeps and during the period ofthe sweep the pump volume exceeds the vibrator means requirements; andf. a controller means connected to the selector means of the manifoldinto the hydraulic lift cylinders and to the vibrator.
 4. A method foroperating a transportable hydraulic seismic transducer comprising: a.transporting a hydraulic seismic vIbrator to a marked location for aseismic source; b. actuating a prime pump to fill the low pressure sideof a hydraulic system and raise the pressure therein to a selectedpressure; c. activating a charge pump while deactivating the prime pumpto fill the hydraulic system; d. activating a main pump to supply at aconstant volume rate a manifold and high pressure accumulator withhydraulic fluid until a selected pressure is developed in the manifoldand the high pressure accumulator on the high pressure side of thehydraulic system; e. actuating a valve on the manifold to introducehydraulic fluid into lift cylinders to lower a vibrator pad into contactwith the earth and then raise the truck from the ground to supply a holddown force on the vibrator pad; f. actuating a controller means coupledto a torque motor of a servo valve to supply hydraulic fluid to thevibrator for producing varying frequencies through a given frequencyrange of a sweep, said high pressure accumulator and main pump providingrequired hydraulic fluid through the manifold to the cylinder during thelow frequency operation of the vibrator and said pump supplying fluidthrough the manifold to the vibrator for producing the high frequencyvibrations of the sweep and to the high pressure accumulator to rechargethe hydraulic fluid portion and to pressurize the pressure portion ofthe accumulator for repeated sweep operations of the vibrator; and g.actuating the valve for the lift cylinders to permit the transportingmeans to be lowered to the ground and to permit fluid to flow into thelift column cylinders to raise the vibrator pad from the earth inpreparation for movement of the portable vibrator to a new sourcelocation.
 5. A transportable hydraulic seismic transducer comprising: a.a transport means for transporting a seismic vibrator to a seismicsource location; b. a vibrator means attached to the transport means; c.a pad rigidily secured to the vibrator means for generating acousticalenergy into the earth responsive to the vibration frequencies of thevibrator means; d. column means connected to the pad and slidinglysecured to the transport means in position to extend substantiallyvertically on opposite sides of the transport means; e. a means carriedby the transport means and connected to the lift columns for raising andlowering the lift columns relative to the transport means and forraising and lowering the transport means as to the lift columns; f. asynchronizing means interconnecting the lift columns and transport meansfor synchronizing the raising and lowering of the lift columns and forequalizing work between the lift columns comprising a synchronizingshaft rotatably attached to the frame of the transport means, and asynchronizing shaft drive means coupled to the lift columns andsynchronizing shaft operatively responsive to movement of the liftcolumns to synchronize their movements and to equalize the work of saidlift columns.
 6. A transportable seismic transducer according to claim5, wherein said synchronizing shaft drive means comprises: sprocketsmounted adjacent each end of the synchronizing shaft, and link chainshaving links engaging the teeth of the sprockets and ends attachedadjacent upper and lower ends of the lift columns whereby the raisingand lowering of the lift columns result in a corresponding movement inthe chains and a driving force on the synchronizing shaft sprockets toimpart a lift synchronizing moment on the synchronizing shaft and a workequalizing force on the lift columns.
 7. A transportable seismictransducer according to claim 6, wherein one of said chains includes aswitch actuating means, and a lift columns control switch supported bythe transport means in the path of the switch actuating means carried bythe chain whereby the lift columns control switch is manipulated by theswitch actuator means to control movement of the lift columns.
 8. Atransportable hydraulic seiSmic transducer according to claim 5 furthercomprising a plurality of limit switches and switch activating meanscoupled to the synchronizing shaft for selectively actuating theswitches to control movement of the lift columns.
 9. A transportablehydraulic seismic transducer comprising: a. a transport means fortransporting a hydraulic seismic vibrator to a seismic source location;b. a vibrator means for producing mechanical vibrations mounted uponsaid transport means; c. a pad rigidly secured to the vibrator forgenerating acoustical energy in an elastic media responsively to thevibrations of the vibrator; and d. a hydraulic system means operativelyconnected to the vibrating means for vibrating the vibrator to producevarying frequencies of a given range of a sweep including: i. ahydraulic fluid pumping means connected to the vibrator manifold forsupplying the manifold with hydraulic fluid at a volume rate requiredfor the vibrator to produce the varying frequencies of the sweep; ii. apressurized storage means coupled to the manifold of the vibratorincluding a high pressure transfer barrier accumulator system having ahydraulic fluid containing portion and a gas pressurized portion, saidfluid portion and pressurized portion being responsive to the hydraulicfluid pumping means and vibrator requirements for alternately receivinghydraulic fluid from the manifold under increasing pressure of thepressurized portion and forcing hydraulic fluid from the fluidcontaining portion into the manifold to maintain the volume of hydraulicfluid required by the vibrator during a sweep; and iii. a control meansconnected to the manifold means for controlling the amount of hydraulicfluid introduced and removed from the vibrator means whereby thevibrator is activated to produce the varying frequencies of the sweep.10. A transportable hydraulic seismic transducer according to claim 9,wherein said means for supplying hydraulic fluid to the manifold of avibrator comprises a source of hydraulic fluid, pump means connected tothe hydraulic fluid source for pumping hydraulic fluid from the sourceat a volume rate between the maximum average and minimum average volumerequired for the vibrator to produce the varying frequencies of thesweep, and a power source connected to the pump.
 11. A method foroperating a transportable hydraulic seismic transducer comprising: a.selectively introducing hydraulic fluid into hydraulic lift cylindersattached to a transport means to lower a vibrator pad into contact withthe earth and lift the transport means to supply a hold down force onthe pad; b. activating a pump for pumping hydraulic fluid at a volumerate less than the maximum average volume required by a seismic vibratorto produce a series of varying frequencies within a given frequencyrange of a sweep into a manifold and a high pressure accumulator or ahydraulic system for a seismic vibrator, said pumping of hydraulic fluidcontinuing throughout the sweep; and c. actuating a servo controlmechanism to selectively introduce hydraulic fluid from the manifoldinto the vibrator for vibrating the pad with said high pressureaccumulator supplying the additional volume of hydraulic fluid requiredby the hydraulic system of the vibrator during one portion of the sweepand storing under pressure the hydraulic fluid excessive to vibratorrequirements during another portion of the sweep.